The present invention relates to a hologram transfer foil for enabling a volume hologram to be applied to any associated member by thermo-compression as well as to a hologram transfer foil useful for prevention of illegal copying of the volume hologram after applied to the associated member.
A volume hologram provides a means capable of recording information in its thickness direction, and recording and reconstructing three-dimensional images. Volume holograms are now fabricated by known fabrication processes. Typically, the volume holograms are used for prevention of illegal copying of ID cards, bank cards, etc., because they are fabricated by precise operations using optical equipment and so are very difficult to fake. In addition, the volume holograms are expressed in interference colors of light and so have an outside appearance hardly achievable by other imaging means. In a typical application taking full advantage of the aforesaid features of volume holograms, a hologram adhesive label, obtained in a film form with an adhesive attached thereto, is applied to a variety of associated members. For instance, JP-A 63-284586 discloses a transfer type hologram of a multilayer structure comprising a substrate, a volume hologram layer and a heat seal layer in this order. In view of prevention of illegal copying using a relief hologram, for instance, Japanese Patent No. 2,934,281 shows a transfer type hologram of a multilayer structure comprising a substrate, a relief hologram layer and a heat seal layer in this order.
In the former, however, the volume hologram layer is basically made up of a photo-cured resin layer whereas the associated member is formed of high-quality paper or the like. Such a material difference often makes it difficult to select a heat-sealing agent showing satisfactory adhesion with respect to both materials, and so this label is applied to only a limited number of application members although depending on the heat sealing agent used. For this reason, the hologram layer peels off at an interface between the volume hologram layer and the heat seal layer or the heat seal layer and the application member, resulting in a high risk of illegal copying.
The latter transfer type hologram has a feature of seeing through characters, images or the like on the application member due to a difference between the volume hologram and the relief hologram. If a colored layer is interleaved between the volume hologram layer and the application member to form a back layer, the contrast of a hologram image can then be enhanced so that high visibility is achievable. However, it is difficult to color the volume hologram per se and so the provision of another colored layer is now under investigation. For instance, the applicant has already filed patent applications Nos. 10-278493 and 11-324980 to come up with the use of a colored adhesive layer. However, the migration of a coloring component into the volume hologram layer becomes a problem because of an adverse influence on hologram recording.
One object of the present invention is to provide a hologram transfer foil enabling a volume hologram to be applied to any desired application member by thermo-compression, which is effective for prevention of illegal copying because the volume hologram layer or the associated member suffers a material breakdown upon the hologram layer being forcibly released after application. Another object of the present invention is to provide a hologram transfer foil capable of ensuring prevention of an adverse influence on the hologram layer of a coloring component in a colored layer functioning as a back layer.